System and method for monitoring and controlling gas plasma processes

ABSTRACT

A system and method for monitoring the conditions in a gas plasma processing system while varying or modulating the RF power supplied to the system, so that resulting signals of the electrical circuits of the system provide information regarding operational parameters of the system or the state of a process. Significant improvements in sensitivity and accuracy over conventional techniques are thereby achieved. In addition, the plasma processing system can be thoroughly tested and characterized before delivery, to allow more accurate monitoring of and greater control over a process, thereby improving quality control/assurance of substrates being produced by the system. The information obtained by the modulation technique can be displayed on a monitor screen, in order to allow an operator to accurately monitor the system/process and diagnose any problems with the system/process.

CROSS-REFERENCE TO OTHER CO-PENDING APPLICATIONS

[0001] This non-provisional application claims priority to applicationSer. No. 09/508,105, filed Apr. 19, 2000, under 35 USC 120, to PCTApplication No. PCT/US98/18498, filed Sep. 17, 1998, under 35 USC 365,and to provisional Application Serial No. 60/059,151, filed Sep. 17,1997 under 35 USC 119(e), the contents of each of which are incorporatedherein by reference. This application is related to “Device and Methodfor Detecting and Preventing Arcing in RF Plasma Systems,” Ser. No.60/059,173, Attorney Docket No. 2312-540-6 PROV, and “ElectricalImpedance Matching System and Method,” Ser. No. 60/059,176, AttorneyDocket No. 2312-539-6 PROV. Both applications are incorporated herein byreference. This application is also related to “Device and Method forDetecting and Preventing Arcing in RF Plasma Systems,” Ser. No.09/508,102, Attorney Docket No. 2312-743-6YA WO, and “ElectricalImpedance Matching System and Method,” Ser. No. 09/508,103, AttorneyDocket No. 2312-741-6YA WO, filed on even date herewith. Both of thosenon-provisional applications are incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates to systems and processes which useelectrically generated gas plasma. The invention is particularlyapplicable to systems and processes which utilize a plasma inmanufacturing solid state and/or semiconductor devices.

[0004] 2. Discussion of the Background

[0005] Many semiconductor or solid state manufacturing processes utilizea gas plasma to perform a fabrication step. This step can be, forexample, a chemical modification or an etching of a thin film, and mayuse chlorine gas or oxygen, among others. Often, particularly in thesemiconductor industry, extremely precise control of the reactionconditions and the timing of the reaction is required. It is thereforeimportant to accurately monitor the plasma conditions, the condition ofthe equipment, and the progress of the reaction.

[0006] Conventional plasma reaction systems have used opticalspectrometry of the optical light emissions from the plasma in order todetect various chemical species produced by the reaction between thesubstrate and the plasma. Concentrations of these species can be used asan indication of the plasma conditions, or as an indication of theprogress of the process being performed with the plasma (e.g., todetermine the end point of the process). However, this technique is notsufficiently precise for certain processes. In particular, the opticaldetection method does not always provide a sufficiently reliable andtimely indication of when a processing step (such as the etching of aphotoresist or a metal layer) is complete.

[0007] Conventional plasma processes systems have also used timing todetermine the end of a step. Several test runs are performed under theconditions to be utilized in an actual manufacturing run, in order todetermine the reaction rate. During the actual manufacturing run, theplasma processing step is performed for a predetermined amount of time,and then terminated. However, slight variations in, e.g., the ambientenvironment, the manufacturing equipment, the plasma, and the workpiececan vary the reaction rates/times, thus making this method less thanoptimal.

[0008] Particularly where the processing step requires only a shortamount of time, accurate determination of the end point can be crucial.For example, during etching of an extremely thin layer, a delay in thetermination of the step can result in the plasma etching into the layerbeneath the layer for which etching is intended. As semiconductorprocesses require increasingly thinner films, and as high density plasmasystems allow for shorter etching and reaction times, it has becomeincreasingly important to accurately determine the time at which aprocessing step is complete.

[0009] In addition, integration densities of semiconductor devices havecontinued to increase, demanding new levels of precision in controllingthe reactive processes used for producing the devices. During aprocessing step, it is increasingly important to carefullycontrol/monitor the conditions of the plasma (e.g., ion density and gasmixture), which directly impact not only rates of reaction, but alsothin film material properties. System conditions, such as thecleanliness of the system, proper assembly/configuration ofelectrical/RF connections, RF matching, age of components, etc., canalso affect the plasma conditions. Accordingly, a system and method areneeded for accurately monitoring and controlling plasma and systemconditions during a given process step, and for detecting the completionof the process step in order to shut down the plasma process at anappropriate time.

[0010] Known references have discussed using the harmonic content of anelectrical signal to determine the condition of the plasma by exploitingthe inherent non-linearity of the plasma. See Miller & Kamon (U.S. Pat.No. 5,325,019 (hereinafter “the '019 patent”)), Gesche & Vey (U.S. Pat.No. 5,025,135 (hereinafter “the '135 patent”)), Patrick et at. (U.S.Pat. No. 5,474,648 (hereinafter “the '648 patent”)), Turner et al. (U.S.Pat. No. 5,576,629 (hereinafter “the '629 patent”)), and Williams &Spain (U.S. Pat. No. 5,472,561 (hereinafter “the '561 patent”)).

[0011] The '135 patent discloses a high-pass filter of a sampledelectrical signal wherein the presence of high frequency contentdetermines the existence of a plasma. The '019 patent uses thefundamental and harmonic frequency components of voltage and currentmeasurements (measured at an electrode within the plasma electricalsystem) to select operating conditions. However, it does not teachcorrelating harmonic content with plasma process input parameters, suchas pressure, RF input, etc. Furthermore, it does not teach controlfunctions based upon the linear and/or non-linear combination ofharmonic amplitude ratios (ratio to the amplitude of the fundamentalfrequency). Likewise, none of the '019, '629, and '561 patents recognizethat information regarding a plasma process can be obtained bymodulating the RF power.

[0012] Several patents address some aspects of intelligent control ofplasma processes. In particular, some patents attempt to characterizethe plasma system performance, generate a database, monitor electricalcomponents during run conditions, and compare to the database todetermine the plasma conditions. For example, Kochel (U.S. Pat. No.4,043,889) addresses this issue. It discloses a method of using apredetermined bias voltage versus pressure characteristic to tune aprocess to ‘optimal’ conditions (in a chamber performing RF sputteringof a thin film). Moreover, Tretola (U.S. Pat. No. 4,207,137), describescontrolling a plasma process.

[0013] Additionally, several patents teach monitoring the electricalproperties of a plasma system and correlating their variation withplasma conditions. For example, Patrick et al. (U.S. Pat. No. 5,474,648)discloses (a) a control method to improve repeatability and uniformityof process and (b) monitoring the power, voltage, current, phase,impedance, harmonic content and direct current bias of the RF energytransferred to the plasma. Additional references describing electricalproperty characterization for plasma processing devices include Logan,Mazza & Davidse, “Electrical characterization of radio-frequencysputtering gas discharge,” J. Vac. Sci Technol., 6, p. 120 (1968);Godyak, “Electrical characteristics of parallel-plate RF discharges inArgon,” IEEE Transactions on Plasma Sci., 19(4), p. 660(1991); andSobolewski, “Electrical characterization of radio-frequency dischargesin the Gaseous. . . ”, J. Vac. Sci. Technol., 10(6) (1992). Forreal-time control of etching processes using multi-variate statisticalanalysis, see Fox & Kappuswamy (U.S. Pat. No. 5,479,340).

[0014] Some patents also discuss monitoring the optical properties of aplasma. Using an optical emission spectrometer, information about thespecies present within the plasma (and their approximate concentration)can be ascertained from monitoring the emission spectrum of the lightpresent. In fact, several spectrometers (or those which comprise arotary grating) may monitor the presence of several species and, hence,provide a plurality of inputs to a plasma process control system. SeeCheng (U.S. Pat. No. 5,160,402) and Khoury, Real-time etch plasmamonitor system, IBM Technical Disclosure Bull., 25(11A) (1983).

[0015] Turner (U.S. Pat. No. 4,166,783) proposes a computer controlsystem for use with deposition rate regulation in a sputtering chamber.The system records the use of the sputtering device and compiles ahistory of its performance. During future use of the device, the pastperformance, age, etc., are incorporated into adjustments made during arun condition.

[0016] Automatic impedance matching systems are also known which employa (quasi-)intelligent controller to monitor an electrical property ofthe plasma chamber. In fact, some systems attempt to obtain somecorrelation between settings for variable reactances (i.e., capacitorsand inductors) and plasma conditions such as the load impedance orplasma chamber input parameters (i.e., RF input power, chamber pressure,etc.). If correlation is obtained, then coarse tuning of the impedancematching also can be obtained. For example, U.S. Pat. No. 5,195,045 toKeane & Hauer presents a method of using predetermined set points fortwo impedance varying devices in order to solve tuning problems duringrun conditions. Additionally, U.S. Pat. No. 5,543,689, to Ohta &Sekizawa, proposes storing match circuit settings from prior use. U.S.Pat. No. 5,621,331, to Smith et al., presents a method for rapidlyadjusting the impedance of a variable impedance device to match (a) theimpedance of a source to (b) the impedance of a load in a plasmaprocessing device. The device includes a plurality of electricalsensors, a photosensitive detector, a data processor, and a memory. The'331 patent correlates (1) variable reactance settings and (2)measurements of chemical species present within the plasma using anoptical emission spectrometer and electrical measurements taken onplasma coupling elements. In this manner, a set of chemistry conditionsmay be selected and tuned by monitoring the variable reactance settings.

[0017] Neural networks have been used for both predication and controlin many areas. A use of neural networks in semiconductor processing topredict the endpoint of an etch process is discussed by Maynard et al.in “Plasma etching endpointing by monitoring RF power systems with anartificial neural network,” Electrochem. Soc. Proc., 95-4, p189-207,1995, and “Plasma etching endpointing by monitoring radio-frequencypower systems with an artificial neural network,” J. Electrochem. Soc.,143(6).

SUMMARY OF THE INVENTION

[0018] In view of the foregoing, it is an object of the invention toprovide a system and method which can quickly and accurately monitor andcontrol a process that uses a gas plasma, e.g., in a processing systemwhich generates a plasma using radio-frequency (RF) power.

[0019] According to one aspect of the invention, the plasma conditionsand system conditions are sensed by varying or modulating one or more ofthe amplitude, phase, and frequency of RF power on an element in thesystem, and by observing characteristics of the resulting responsesignals of the same element, and/or one or more other elements in thesystem. The “elements” are electrical components of the system, moreparticularly plasma coupling elements such as electrodes, a bias shield,an inductive coil or an electrostatic chuck. The electrical componentscan also include a probe or another sensor utilized to obtain signals inresponse to modulation of the power.

[0020] In one exemplary embodiment, each of the modulated signals isobserved at a node of a power delivery circuit, which can include, forexample, an electrical matching network. The measured responseinformation is then compared with stored data obtained for knownconditions, and the system conditions are determined as corresponding tothe conditions under which the stored data (which most closely resemblesthe measured data) was obtained.

[0021] In a presently preferred embodiment, in order to meaningfullyutilize information obtained by modulating the power to one or more ofthe system components, the processing system is characterized with aseries of test runs. The term “test run” is used herein to mean a testof a processing system performed for the purpose of characterizing thesystem. The test run can be performed under conditions similar to thoseunder which a production run would be performed. In addition, the testrun can correspond to conditions to be utilized in performing adiagnostic test of equipment to be utilized in a processing run, so thatinformation obtained in the test run can be utilized to determine thecondition of equipment, for example, before a process step commences. Atest run is performed by operating the system under a given/known set ofplasma conditions and system conditions, applying modulated RF power toone or more of the electrical components (more particularly the plasmacoupling elements), and measuring the resulting modulation responsesignals. A series of test runs are performed by systematically varyingthe plasma conditions and/or system conditions so that response signalsare obtained and correlated with the various conditions, therebyproviding response signal data which can be stored as characteristic ofthe known conditions. For example, the power, pressure, gas mixture, ormaterial being processed can be varied, and the effects of thesevariations on the modulation response signals can be determinedempirically. Additional conditions varied during a test/characterizingrun can include cleanliness (time or cycles since cleaning/maintenancewas performed), age of components, ambient temperature and/or humidity,etc. It is to be understood that the number of condition variables forwhich data is obtained can vary depending upon, e.g., the extent towhich the profiles will be utilized throughout a processing run, levelof sophistication/control desired, and budgetary constraints. Forexample, a relatively simple system might utilize modulation responseinformation only to detect the end point of a process, or to indicatethe cleanliness of a system. A more complex system can consideradditional conditions/variables throughout a process.

[0022] The response information obtained during a test run forms adatabase, which includes a multi-dimensional array of data points, eachdata point containing information regarding a characteristic, such asthe amplitude or phase, of one modulated signal component. For a givenset of plasma and system conditions, the data points can be groupedtogether to form a modulation profile. The term “modulation profile” isused herein to mean a set of data associated with a set ofprocess/system conditions, which represents the characteristics of thesignals caused by modulating the RF power to one or more plasma couplingelements. Each set of process conditions stored in the database isthereby associated with (i.e., linked to) a modulation profile.

[0023] The data obtained during the test run is then utilized during anactual production run, in which the process conditions can bedetermined/inferred by modulating the RF power on various plasmacoupling elements, observing the effects of the modulation on signalsfrom the same, or other, plasma coupling elements, and constructing anobserved modulation profile from these measurements. To determine thecurrent process conditions, the system uses either (1) the storedmodulation profile (i.e., the profile from the database obtained duringtest runs) that most closely matches the observed modulation profile, or(2) a neural network which predicts the current process conditions fromthe observed modulation profile. When using the first method, thedatabase links this stored profile to a set of stored processconditions. The current process conditions are thus determined/inferred,based on these stored process conditions. For example, in a plasmaetching system having a plasma coupling element, the RF power beingsupplied to this element can be amplitude modulated at a certainmodulation frequency and modulation amplitude. The resulting modulationresponse signal is observed by measuring the voltage at, e.g., a node ofthe power delivery circuit. The amplitude of the modulation responsesignal can have one value during the etching of a film and a secondvalue after the etching has been completed, based upon empirical dataobtained in a test run. The plasma state (and therefore, the processstate) during etching is associated with a first modulation profile, andthe plasma state (and the process state) after etching is associatedwith a second modulation profile. Each of the profiles in this examplewould contain a single data point, corresponding to the amplitude of themodulation response signal. During a processing run, the modulationresponse signal can then be utilized to determine the end point of anetching process, i.e., when the second modulation profile is detected.When using the second method, the neural network determines the endpoint of an etching process. An observed modulation profile is appliedas an input to the neural network to determine when etching is completewithout requiring an exact match of a modulation profile.

[0024] According to the present invention, it has been recognized thatthe characteristics of the aforementioned modulation response signalscan be sensitive to changes in plasma and system conditions, and theprogress of a reaction. Consequently, a more accurate or complete“picture” of the process conditions can be obtained as compared withconventional systems. In addition, since process/system conditions canbe extremely well-characterized, deviations from the desired processconditions can be accommodated or cancelled out by modifying thecharacteristics of the RF power. Further, when using a neural network,small errors are naturally compensated for by the neural network.Alternatively, when it is determined that conditions are unsuitable,corrective action can be taken, while preventing or minimizing damage tothe equipment or substrates being processed. Therefore, improvedconsistency/repeatability of the process and resulting product isachieved. According to another aspect of the invention, a wide varietyof process conditions and/or observed modulation effects/responses canbe displayed on a monitor screen, so as to rapidly give an operatoruseful information regarding the process or status of the process.

[0025] The invention offers several advantages over conventionalsystems. In particular, by modulating the RF power and observing themodulation response signals in the electrical circuits of the system,the current characteristics of a plasma can be determined to a greaterdegree than optical detection or timing methods used in conventionalsystems. In addition, the invention allows plasma processing systems tobe thoroughly tested and characterized under well-controlled conditionsbefore delivery or use in manufacturing substrates, so as to providequality assurance of the systems, as well as insuring the accuracy ofthe database used to analyze the modulated signals. These features allowfor more precise control of the manufacturing processes, therebyimproving the quality assurance of the wafers (or other substrates)being produced. Moreover, improving the quality assurance results infewer defective wafers, so that the manufacturing yield is increased andmanufacturing costs are decreased. Furthermore, the information obtainedby the modulation technique can be displayed in an easily-understandableformat, on a monitor screen, in order to allow an operator to accuratelymonitor the system or a process being performed and to detect problems.This results in improved reliability and reduced risk of operator error.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] A more complete appreciation of the invention and many of theattendant advantages thereof will become readily apparent from thefollowing detailed description, particularly when considered inconjunction with the accompanying drawings, in which:

[0027]FIG. 1 is a block diagram of a plasma processing system;

[0028]FIG. 2 is a schematic diagram of a circuit, including a matchingnetwork, used to deliver power to a plasma;

[0029]FIG. 3 is a block diagram representing a plasma coupled to threeplasma coupling elements;

[0030] FIGS. 4A-4C are exemplary graphs of portions of frequency-domainspectra of voltage amplitudes measured at plasma coupling elements;

[0031] FIGS. 4D-4F are exemplary graphs of portions of frequency-domainspectra of voltage phases measured at plasma coupling elements;

[0032]FIG. 5 is an exemplary graph of a portion of a frequency-domainspectrum of voltage amplitude measured at a plasma coupling element;

[0033]FIG. 6A is a first screen display;

[0034]FIG. 6B is a second screen display;

[0035]FIG. 7A is a circuit diagram of a demodulator with in-phase andquadrature channels;

[0036]FIG. 7B is a schematic illustration of a DSP-based demodulator;

[0037]FIG. 8 is a block diagram of a computer system for use as amonitor/controller or a central process controller;

[0038]FIG. 9A is a schematic illustration of a trained neural networkused to determine current process conditions of a plasma process;

[0039]FIG. 9B is an example of a flowchart of a procedure used todetermine current process conditions of a plasma process, based onmodulation profiles stored in a database;

[0040]FIG. 10 is an example of a flowchart of a procedure used tocollect modulation sideband information for use in a plasma processingsystem;

[0041]FIG. 11A is a graph showing the first five harmonics in thefrequency spectrum taken from voltage measurements sampled at theprimary conductor of a plasma system, after removing noise;

[0042]FIG. 11B is a graph showing the spectrum of FIG. 11A, but beforeremoving the noise;

[0043] FIGS. 12A-12C are graphs of harmonic amplitude ratios for thesecond harmonic when several process parameters are varied; and

[0044] FIGS. 13A-13D are graphs of harmonic amplitude ratios for thethird harmonic when several process parameters are varied.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] Referring now to the drawings, wherein like reference numeralsdesignate identical or corresponding parts throughout the several views,FIG. 1 illustrates an embodiment of a plasma processing system, whichincludes a monitor/controller 1 and a modulation signal generator 3.Although the exemplary embodiments of the present invention aredescribed in the context of systems using RF power, it is to beunderstood that the invention can also be utilized in systems in whichthe power source operates at other frequencies or frequency ranges. Inaddition, although the system in FIG. 1 includes both inductive andcapacitive plasma coupling elements, it is to be understood that variousaspects of the present invention can also be advantageously utilized inother types of systems. For example, the invention can also be utilizedin systems which do not include inductive plasma coupling elements(e.g., sputtering systems).

[0046] In the FIG. 1 arrangement, gases, such as oxygen and chlorine,are introduced into a processing chamber 33 through gas inlets 123. Thegases are excited into a plasma state using RF power, in order to reactwith a substrate such as a semiconductor wafer 40. RF sources 2A, 2B,and 2C send RF power into the local oscillator (LO) terminals of mixersM1, M2, and M3, respectively. A power varying controller, such as amodulation signal generator 3, sends modulation signals into theintermediate frequency (IF) terminals of mixers M1, M2, and M3,respectively. As is well known in the art, the signal provided at theradio frequency (RF) terminal of a mixer contains the product of thesignals sent into the LO and IF terminals of the mixer. If the IF signalcontains a sinusoidal component, with no DC component, the frequencyspectrum of the modulated signal at the RF terminal of the mixercontains two components at sideband frequencies (i.e., frequenciesadjacent to the LO frequency). One sideband frequency is equal to the“difference frequency” of the LO frequency and the IF frequency (i.e.,the LO frequency minus the IF frequency). The other sideband frequencyis equal to the “sum frequency” of the LO and IF frequencies (i.e., theLO frequency plus the IF frequency). If the IF signal also contains a DCcomponent, the modulated signal contains a component at the localoscillator (LO) frequency, in addition to the aforementioned sidebandcomponents. In addition, if the IF signal contains components at anumber of different frequencies, the modulated signal containsadditional sideband components. Each additional sideband component is ata frequency corresponding to the sum or difference of the LO frequencyand the frequency of one of the IF components. Each additional componentin the IF signal produces two additional sidebands, one below the LOfrequency and the other above the LO frequency.

[0047] In a presently preferred embodiment of the invention, the LOfrequency is 13.56 MHZ, while the frequencies of the IF components aresignificantly lower (e.g., below 1 MHZ), which causes the differencesbetween the sideband frequencies and the LO frequency to besignificantly smaller (e.g., less than 1 MHZ) than the LO frequency.That is, in comparison with the LO frequency, the sideband sidebandsappear close in frequency to the LO component.

[0048] The modulation signal generator 3, and the frequencies andamplitudes of modulation produced by it, are controlled bymonitor/controller 1. Mixers M1, M2, and M3 provide, at their RFterminals, modulation response signals, which are sent into monitoringsensors, such as phase/amplitude detectors 11, 12, and 13, respectively.The phase/amplitude detectors provide information regardingcharacteristics of various frequency components of the modulationresponse signals (i.e., the signals from a set of plasma couplingelements). Each characteristic of a frequency component can correspondto one of two possible characteristic types, the two possiblecharacteristic types being an amplitude and a phase. Frequencycomponents of interest include response components caused by varying theamplitude, frequency and/or phase of the RF power supplied by one ormore of the RF sources. By using a mixer, the amplitude of the RF powercan be varied. In the illustrated embodiment, the plasma couplingelements include coil 30, electrostatic chuck 31, and bias shield 32.The RF power passes through the respective phase/amplitude detectors andis sent to the respective plasma coupling elements. The outputs of thephase/amplitude detectors (11, 12 and 13) are sent into themonitor/controller 1 for analysis. A central process controller 20controls the devices used for this processing step, as well asprocessing equipment 100 for other steps.

[0049] Alternatively, a power varying controller may vary the amplitude,frequency and/or phase of an RF source by sending a control signal intocontrol circuitry internal to the source or control circuitry externalto the source. The resulting RF power can be amplitude modulated, aswould result from using a mixer, but may also have a combination ofvarying amplitudes, frequencies and/or phases.

[0050] In one embodiment of a phase/amplitude detector, the phase andamplitude of a given response component of a plasma signal aredetermined by demodulating the signal component into “in-phase” and“quadrature” components. FIG. 7A illustrates an example of a circuitused to perform this operation. An input voltage V_(in) is sent into therespective RF terminals of an in-phase mixer MI (which is part of anin-phase channel 71) and a quadrature mixer MQ (which is part of aquadrature channel 72). A local oscillator source LOD provides a signalwhich is sent into the LO terminal of mixer MI. The signal from LOD isalso sent into a phase-shifter φ90, which shifts the phase of the LOsignal by 90° and sends it into the LO terminal of mixer MQ. The IFterminal of mixer MI is sent into a low-pass filter, which includes aresistor RI and a capacitor CI. The resulting downconverted and filteredoutput V_(OI) represents the in-phase component of the input signalV_(in). The IF output of mixer MQ is sent into a low-pass filter, whichincludes a resistor RQ and a capacitor CQ. The resulting downconvertedand filtered signal V_(OQ) represents the quadrature component of theinput signal V_(in). The amplitude |V_(in)| of the input voltage can becalculated by the formula:

|V _(in)|={square root}{square root over ((V _(OI))²+(V _(OQ))²)}

[0051] The phase (φ) V_(in), relative to the phase of the demodulationlocal oscillator LOD can be determined from the equation:

φ=tan⁻¹(V _(OQ) /V _(OI))

[0052] The specific modulation response signal component which is beingmeasured can be selected by choosing the frequency of local oscillatorLOD. It should be noted that while the circuit illustrated in FIG. 7A isone method of determining amplitude and phase of a signal component,other techniques may be used, as would be readily apparent to oneskilled in the art. As shown in FIG. 7B, in a presently preferred formof the invention, the monitor/controller 1 (FIG. 1) includes ananalog-to-digital (A/D) converting unit 71A and a digital signalprocessing unit (DSP) including a non-volatile data storage device, suchas an EPROM or a disk drive. The A/D converting unit 71A includes pluralA/D convertors 1126 that receive analog signals from the respectivephase/amplitude detectors, and convert the analog signals into digitalnumbers. The DSP (or a properly programmed CPU) analyzes and organizesthis information and stores it in the non-volatile data storage device.Such a conversion includes performing a Fast Fourier Transform (FFT) onthe input to convert the input from the time domain to the frequencydomain. The DSP (or CPU) also retrieves data from the storage device andcompares it with new data being received from the phase/amplitudedetectors.

[0053] According to an exemplary embodiment, the monitor/controller is acomputer system, illustrated schematically in FIG. 8. The computersystem 1100 has a housing 1102 which houses a motherboard 1104 whichcontains a central processing unit (CPU) 1106, memory 1108 (e.g., DRAM,ROM, EPROM, EEPROM, SRAM and Flash RAM), and other optional specialpurpose logic devices (e.g., ASICs) or configurable logic devices (e.g.,GAL and reprogrammable FPGA). In addition, according to the invention,the computer system contains analog-to-digital (A/D) inputs 1126 forreceiving signals from the various phase/amplitude detectors 11, 12, and13 (FIG. 1). The computer also contains communication ports 1128 (FIG.8) for communicating with a central process controller 20, a modulationsignal generator 3 and RF sources 2A-2C (FIG. 1). The computer 1100(FIG. 8) further includes plural input devices, (e.g., a keyboard 1122and mouse 1124), and a display card 1110 for controlling monitor 1120.In addition, the computer system 1100 includes a floppy disk drive 1114;other removable media devices (e.g., compact disc 1119, tape, andremovable magneto-optical media (not shown); and a hard disk 1112, orother fixed, high density media drives, connected using an appropriatedevice bus (e.g., a SCSI bus or an Enhanced IDE bus). Although compactdisc 1119 is shown in a CD caddy, the compact disc 1119 can be inserteddirectly into CD-ROM drives which do not require caddies. Also connectedto the same device bus or another device bus as the high density mediadrives, the computer 1100 may additionally include a compact disc reader1118, a compact disc reader/writer unit (not shown) or a compact discjukebox (not shown). In addition, a printer (not shown) can also provideprinted copies of important information related to the process, e.g.,sideband phases and amplitudes, RF power levels, and process conditions,as determined from analysis of the sideband components, as discussed infurther detail hereinafter. Operation of the plasma controller, such asrecords of RF power levels and arcing behavior can also be displayedand/or printed.

[0054] The computer system further includes at least one computerreadable medium. Examples of such computer readable media are compactdiscs 1119, hard disks 1112, floppy disks, tape, magneto-optical disks,PROMs (EPROM, EEPROM, Flash EPROM), DRAM, SRAM, etc.

[0055] Stored on any one or on a combination of the computer readablemedia, the present invention includes software for controlling both thehardware of the computer 1100 and for enabling the computer 1100 tointeract with a human user and the controlled system(s). Such softwaremay include, but is not limited to, device drivers, operating systemsand user applications, such as development tools. Such computer readablemedia further includes a computer program, according to the presentinvention, for operating the monitor/controller.

[0056] The monitor/controller can serve as a remote computer, and canallow an operator to “log on” to a host computer which may be a centralprocess controller 20 (FIG. 1) controlling not only this particularprocess but other processes in the fabrication line which use their ownequipment 100. The host computer, which can be of a form similar to thecomputer system of FIG. 8, can restrict the possible choices that theoperator is allowed to make while performing the process, thus reducingthe risk of operator error, and allowing for the employment ofless-skilled operators without harming the control over the process.Likewise, in an alternate embodiment, the plasma controller iscontrolled through a GUI, such as a client-server program or using a WWWinterface (including CGI scripts, ActiveX components and Javascript).

[0057] As should be apparent, the invention may be convenientlyimplemented using a conventional general purpose digital computer ormicroprocessor programmed according to the teachings of the presentspecification, as will be apparent to those skilled in the computer art.Appropriate software coding can be prepared based on the teachings ofthe present disclosure, as will be apparent to those skilled in thesoftware art. The invention may also be implemented by the preparationof application specific integrated circuits or by interconnecting anappropriate network of conventional component circuits.

[0058]FIG. 3 is a block diagram of an arrangement according to theinvention which includes three plasma coupling elements E1, E2, and E3,coupled to a plasma, as well as three independent phase/amplitudedetectors PA1, PA2, and PA3, which measure the phase and amplitudes ofthe voltages V₀₁-V₀₃ on the plasma coupling elements. Also shown is amonitor/controller 1, which receives phase and amplitude informationfrom each of the phase/amplitude detectors (which thus act as monitoringsensors receiving response signals from the plasma coupling elements).

[0059] The RF signals sent into plasma coupling elements E1, E2, and E3are modulated at modulation frequencies F_(M1), F_(M2), and F_(M3),respectively. In one embodiment, E1, E2, and E3 are a plasma couplingcoil 30, an electrostatic shield or bias shield 32, and a wafer holdingchuck 31. Exemplary operating values of F_(M1), F_(M2), and F_(M3) are240 kHz, 116 kHz, and 500 kHz, respectively. As shown in FIGS. 4A-4F,the modulation has the effect of producing sideband signals (i.e.sideband components) surrounding the fundamental frequency on each ofoutput voltages V₀₁, V₀₂, and V₀₃, corresponding to the measuredvoltages on plasma coupling elements E1, E2, and E3, respectively. Eachoutput voltage contains a component at the fundamental frequency of theRF source and may contain components at harmonics of this fundamentalfrequency. Adjacent in frequency to each component at the fundamentaland harmonic frequencies are the sideband components.

[0060] FIGS. 4A-4C illustrate an exemplary spectrum of signal amplitudesof components of voltages measured at a plasma coupling element.Components appear at the frequencies f_(F)−f_(M3), f_(F)−f_(M2),f_(F)−f_(M1), f_(F), f_(F+f) _(M1), f_(F)+f_(M2), and f_(F)+f_(M3),where f_(F) is the fundamental frequency and f_(M1), f_(M2), and f_(M3)are the aforementioned modulation frequencies. FIGS. 4D-4F illustratethe respective phases of the signals shown in FIGS. 4A-4C. Forsimplicity, only the frequency range near the fundamental frequency isshown in these figures. The frequency range near each harmonic alsocontains sideband signals as illustrated in FIG. 5, which is a graph ofthe amplitude of V₀₁ over a wider frequency range than that of FIGS.4A-4F. For example, the frequency range near the second harmonic f₂contains components at the frequencies f₂−f_(M3), f₂−f_(M2), f₂−f_(M1),f₂, f₂+f_(M1), f₂+f_(M2) and f₂+f_(M3). The graph of FIG. 5 shows notonly the frequency range near the fundamental frequency, but also thefrequency ranges near the lowest five harmonics.

[0061] Each sideband component has a phase, relative to that of thecomponent at the fundamental frequency, and an amplitude. The phase andamplitude of the sideband component can depend upon several factors,including the plasma conditions (e.g., ion density, gas mixture, and gaspressure), the system conditions (e.g., proper assembly of RFconnections and other components, the thickness of accumulated reactionproducts, aging of the system or system components, RF matching, and/orother contamination of or damage to the system), the particular plasmacoupling element receiving the corresponding modulated RF power, theparticular plasma coupling element being observed, and the progress ofthe reaction (e.g., whether or not an etching step is complete).

[0062] The observed electrical signals or modulation response signals ofthe plasma coupling elements can be received, e.g., from a node of apower delivery circuit, one example of which is illustratedschematically in FIG. 2. In this example, the power delivery circuitincludes an RF source 2 which sends power through a cable 70 into amatching network MN. The matching network MN, which in this exampleincludes an inductor L and variable capacitors C1 and C2, electricallymatches the output impedance R_(S) of the source to the impedance of aload 300. The load 300 is a plasma coupling element, which receives theRF power from the RF source. In accordance with one arrangement, theelectrical signals measured by the monitor/controller (represented as 1in FIG. 1) are received from a node of a matching network of the powerdelivery circuit (FIG. 2). Alternatively, the observed electricalsignals or modulation response signals of a plasma coupling element canbe more directly obtained, e.g., by obtaining a signal directly from theplasma coupling element. It is to be understood that signals containinguseful information could be received from other elements of a plasmaprocessing system. Other elements which could be utilized to providesignals include, but are not limited to, an RF source and an antenna orprobe coupled to the plasma (e.g., with the probe or antenna disposed inthe process chamber). In addition, it is to be understood that signalscan be obtained from one element or plural elements in order to provideinformation regarding the conditions or state of the process withoutdeporting from the invention.

[0063] The monitor/controller 1 analyzes the relative amplitudes andphases of the sideband components and constructs a modulation profilecorresponding to the current conditions of the plasma and/or the systemequipment. The amplitude spectrum of V₀₁ illustrated in FIG. 5 contains42 signal components, each with a measurable amplitude. Therefore, thisspectrum can be used to obtain at least 42 data points. However, thiscould be only a small part of a complete modulation profile. The profilecould also contain data points for the phase of V₀₁, as well as theamplitudes and phases of V₀₂ and V₀₃. In addition, although the profileis illustrated only up to the sixth harmonic in FIG. 5, it could alsocontain data points at higher harmonics. Furthermore, although thisexample uses only three fixed modulation frequencies, F_(M1), F_(M2),and F_(M3), for the three plasma coupling elements, respectively, amodulation profile may contain data points corresponding to a variety ofdifferent modulation frequencies. As discussed earlier, the amount ofinformation obtained and utilized can vary depending upon the level ofsophistication of a particular system, and whether the system isutilized for monitoring a limited number of conditions (e.g., end pointdetection) or for comprehensively monitoring a wide variety ofconditions throughout a process.

[0064] The current patent has proposed two primary approaches to theintelligent control of a plasma process; namely, (1) the use of a storedmodulation profile (i.e., the profile from the database obtained duringtest runs), or (2) a neural network. Both approaches use a matrix oftest runs to characterize the behavior of the plasma system. The firstapproach stores modulation profiles representative of the plasmaconditions (which could later be extracted from the database during runconditions). The second electrical properties (such as the modulationprofiles) of the system to train the neural network on the normalbehavior of the plasma system.

[0065] Analysis according to the present invention will be discussedbelow in terms of profiling techniques and neural network processes.However, it should be evident to one of ordinary skill in the art thatthe modulation profile can also be applied to other intelligent controlsystems such as fuzzy logic or expert systems. Outputs of a fuzzy logicsystem have an advantage of describing conditions generally, e.g.,medium gas mixture, low pressure or high pressure.

[0066] According to the profiling aspect of the invention, by observingthe modulation profile during a processing run, and comparing thisobserved profile to known profiles in a preexisting database,information regarding the process conditions and/or the progress of aprocessing step can be determined. The set of modulation profiles whichis characteristic of the processing system is stored as an array of datapoints, each corresponding to a specific set of parameter values. Theparameters representing a specific set of process conditions indicatewhich modulation profile is being referenced. The parameters specifyingwhich portion of a profile is being referenced indicate a specificharmonic or fundamental frequency, a specific plasma coupling elementfor which the signal is being modulated, a specific plasma couplingelement which is being observed, specific values of phase and amplitudeof the RF power, and/or specific values of the variable elements in thematching networks.

[0067] By way of example, a “before or after” parameter B indicateswhether a modulation profile corresponds to the process before thecompletion of an etching step (B=0) or after the completion of anetching step (B=1). A “which harmonic” parameter H indicates whichharmonic is being referred to within this modulation profile. Forexample, H=1 refers to the fundamental, while H=2 refers to the secondharmonic, and so on. A “which sideband” parameter S refers to a specificsideband near the aforementioned harmonic. For example, S=1 refers tothe sideband closest to, and above, the specified harmonic, S=−1 refersto the sideband closest to, and below, the specified harmonic, S=2refers to the next furthest sideband above the specified harmonic, S=−2refers to the next furthest sideband below the specified harmonic, andso on. By specifying these three parameters, a data point in thedatabase is uniquely identified, allowing the data to be retrieved. Inthis example, the data is the amplitude of the specified sideband. Morespecifically, the amplitude |V(B,H,S)| of a specified sidebandcorresponding to a specified process condition depends upon whichsideband is referenced and which process condition is specified. Forexample, |V(0,2,1)| may equal 1 mV, while |V(1,2,1)| equals 2 mV. Thisindicates that the first sideband above the second harmonic before theetching step is completed has an amplitude of 1 mV, whereas the samesideband after the completion of the etching step has an amplitude of 2mV. As should be readily apparent that, since the system of this exampleconsiders three parameters (B,H,S), the data can be organized accordingto these three parameters in a three-dimensional array. If an additionalparameter, such as gas pressure, is considered, the data is organizedinto a four-dimensional array. If still another parameter, such as theproportion of a specific gas within the gas mixture, is considered, thedata is organized in a five-dimensional array. However, the data isusually used in a reverse process. As an example, after measuring anamplitude of 1.1 mV, the system can cycle through all B values for afixed pair of H and S values to determine which known state the systemcurrently resembles. By doing so with the parameters above, the systemcan determine that the current amplitude (1.1 mV) is closer to thestored “before” condition (1 mV) than the stored “after” (2 mV)condition.

[0068] The number of dimensions of this array is dependent upon thenumber of modulation parameters required for determining the informationdesired regarding the state or conditions of the process or of thesystem. For example, if the data is organized by every possiblecombination of pressure, relative proportions of two different gases, RFpower levels into each of plasma coupling elements E1, E2, and E3,reaction progress B, harmonic H, and sideband S, the database willcontain a seven-dimensional array of data. Like in the three-dimensionalexample, the system can use less than all seven parameters to index thedatabase to find all profiles with those characteristics. Then, theamplitude data can be used to determine which profile (most closely)matches thereby giving an estimate of current conditions. The parametersmentioned above are cited only as examples, and it is to be understoodthat the invention is not limited to these parameters. Other parametersmay be utilized, including, but not limited to, RF frequencies, relativephases of the power waveforms received by the plasma coupling elements,and the values of the tunable elements in the matching networks.

[0069] An exemplary procedure for obtaining and storing data in thedatabase is illustrated in FIG. 10. In this example, a system with threeseparate plasma coupling elements is tested and characterized bothbefore and after a process is complete using a variety of differentcombinations of power levels supplied to the three plasma couplingelements. For simplicity, other input parameters such RF matching, areassumed to be constant during the process, and output parameters ofinterest, if any, such as temperature, cleanliness, are periodicallymeasured. In steps 700 and 701, the system parameters are initialized toa set of initial values. Then, the power levels supplied to the threeplasma coupling elements are incremented by predetermined amounts (steps702, 703, and 704). Once the power levels are set, the RF power sentinto at least one of the plasma coupling elements is modulated and thephases and amplitudes of the resulting sidebands are measured (Step705), along with output parameters discussed above. Then, in step 706,this sideband information, and any of the output parameters, and anindication of whether or not the process had completed are stored in thedatabase, along with the values of the power levels supplied to therespective plasma coupling elements. If in step 710 it is determinedthat the current value of P1 is the final value which is to be tested(i.e., the maximum value of P1 to be tested), the procedure continues tostep 708. If not, the procedure returns to step 704, at which point thepower level P₁ supplied to the first plasma coupling element isincremented by a predetermined step and the measurement loop is repeatedwith the new value of P₁. In step 708, P₁ is set to its initial valueand, if the current conditions do not correspond to the final level ofP₂ (step 709), the procedure returns to step 703, at which point P₂ isincremented by a predetermined amount and the measurement loop isrepeated for this value of P₂. If, in step 709, P₂ is the final value,the procedure continues to step 730, which resets P₂ to its initialvalue, at which point the procedure continues to step 712 (which checksto determine whether or not the current value of P₃ is the final value).If P₃ is not the final point, the procedure returns to step 702, atwhich point P₃ is incremented by a predetermined amount, and themeasurement loop is repeated with the new value of P₃. In step 712, ifP₃ is the final value, the procedure continues to step 713, at whichpoint, if there are no other system parameters (i.e., parameters otherthan the various levels of RF power) to be investigated, the procedureis terminated (step 715). If there are other parameters of interest(e.g., RF matching parameters), the procedure continues to step 714, atwhich point the other parameters are changed and the procedure repeatsitself, starting from step 701.

[0070] It is to be understood that the procedure of FIG. 10 representsone example in which only RF power levels are varied, and it should bereadily apparent to those skilled in the art that other parameters canalso be varied and other variation sequences can be utilized duringcharacterization of the system. For example, the power can be heldconstant while another condition such as gas flow rate is varied.

[0071] An example of a processing step which can be analyzed by theinvention is the etching of an aluminum metallization layer on a siliconsubstrate. Prior to using the system for this process in a productionrun, modulation profiles characteristic of the processing system areobtained by performing a series of test runs of the system. Some of thetest runs are performed under conditions identical to those of aproduction run during etching, and other test runs are performed underconditions matching those of a production run after completion ofetching. This data can be obtained empirically in the preproductionstage of the system so that the data can be stored in themonitor/controller 1 (in FIGS. 1 and 3) or the central processcontroller 20 (in FIG. 1) when the system is manufactured.Alternatively, for existing equipment, data can be obtained for thattype of equipment and provided in a controller/memory module so that theinvention can be utilized on a retrofit basis. When using a neuralnetwork, the input parameters of the measured profiles are fed into atrained neural network as shown in FIG. 9A. The neural network istrained to predict “normal” and “complete” states using storedmodulation profiles and known desired outputs. Any appropriate trainingalgorithm, such as backpropagation, can be used. Additional details ontraining neural networks can be found in The Roots of Backpropagation byPaul Werbos, Ph.D. Training cycles are repeated until the networkproperly identifies the normal and complete state from the inputs. Asevident to one of ordinary skill in the art, there is an input layer, anoutput layer, and at least one hidden layer, and the number of neuronsin each layer may vary. Likewise, the modulation profiles may be used todetect other states, such as minor or severe arcing.

[0072] When using profiling, during an actual production run, themeasured modulation profiles are compared to the profiles stored in thedatabase. In this example, most of the process parameters, such as gasflow rate, and RF power levels, are kept constant, for simplicity. Theonly parameter varied is the progress of the reaction (i.e., whether ornot it is finished). The monitor/controller 1 repeatedly measures themodulation profile of the process as the reaction progresses. During theetching of the aluminum, the plasma gas mixture contains a certainpercentage of aluminum, whereas, after the etching process hascompletely removed portions of the aluminum film (thereby exposing thesilicon), the gas mixture contains less aluminum. Depending on theprocess, the gas mixture may, in fact, contain a certain percentage ofsilicon once the silicon has been exposed, particularly after thecompletion of the aluminum etching step.

[0073] Due to the aforementioned changes in the composition of theplasma gas, the process during the etching of the aluminum has adifferent modulation profile than the process after completion of theetching. Therefore, the monitor/controller 1 is able to determine whenthe end of this processing step has occurred. An indication is given toa human operator at this time and/or a signal is sent to a centralprocess controller 20, indicating that this processing step should beterminated and the next step should be started. The process may alsohave separately distinguishable intermediate steps which could also beseparately identified in an alternate embodiment, either by profiling orby a neural network.

[0074] The procedure for monitoring the above exemplary process usingprofiling is illustrated in the flowchart of FIG. 9B. First, the etchingprocess is started (step 900) and the RF power is modulated (step 902).Then, in step 904, the monitor/controller measures the phases andamplitudes of the sidebands so as to construct a measured modulationprofile in step 906. At this point, in step 908, the monitor/controllersearches the database for a modulation profile that matches the measuredmodulation profile. If a match is found (step 910), the procedurecontinues to step 912. If no match is found, the procedure continues tostep 916 at which time a warning signal is produced or, alternatively,the sensed profile can either be matched with the stored profile it mostnearly resembles or an interpolation operation can be performed. In step912, the monitor/controller checks to see if the matching profilecorresponds to the end of the etching step. If so, the procedurecontinues to step 920. If the matching profile does not correspond toexpected conditions for the end of etching, the procedure continues tostep 914. In step 914, the monitor/controller checks to ensure that thematching profile corresponds to acceptable process conditions forpartially completed etching. If so, the procedure returns to step 904and repeats the measurement sequence. If not, the procedure continues tostep 922.

[0075] In steps 916, 920, and 922, important information is given to theoperator (or the central process controller 20 at FIG. 1), whereupon theprocedure of FIG. 9B is terminated. Step 916 warns the operator that noacceptable matching profile has been found in the database, indicatingthat the process is in an unknown state. Step 920 notifies the operatorthat the etching is complete. Step 922 warns the operator that, althoughthe process is in a known state, it is not in a suitable state. Itshould also be noted that, while this procedure represents an exemplarymethod of monitoring the process conditions, variations thereof arepossible as should be readily apparent to those skilled in the art.

[0076] According to another aspect of the invention, the earlierdescribed procedure (illustrated in FIG. 10) of accumulating the datawhich characterizes the system is automated. This procedure can beperformed, e.g., during development of the system (i.e., before aproduction model is produced), during production of the system (i.e.,before the system is shipped to end-users), or after production if themonitor/controller is to be provided on a retrofit basis. In either casethe monitor/controller, as shipped or retrofit, contains the entiredatabase. This feature is advantageous in that, aside from providingadded convenience to the end-user, it is also beneficial for qualityassurance, since the manufacturer has greater control over the datacollection and characterization procedure. By avoiding the need foron-site characterization, the manufacturer can insure that only highlyexperienced, qualified personnel perform the characterization procedure.As a result, the chance of operator error is reduced, and theconsistency and repeatability of the process is improved. This aspectcan become particularly advantageous in preventing damage to expensivesemiconductor wafers or equipment components.

[0077] According to an optional aspect of the invention, data can beinterpolated between modulation profiles of the database to obtainfurther detailed information regarding the process/system conditionsduring a processing run. The neural network system performsinterpolation automatically based on the weights between neurons. Usingprofiling, an interpolation method is used as described below. During aprocessing run, the aforementioned modulated RF power is supplied to theinputs of the plasma coupling elements of the system. A modulationprofile of the current state of the process is obtained by measuring theabove-described sideband components. To determine the current state ofthe process, the array of data determined from the measured sidebandcomponents (i.e., the measured modulation profile) is first compared tothe stored profiles kept in the database. The stored profile that mostclosely matches the measured profile is used as an approximation of themeasured modulation profile. Since each profile in the database isassociated with a specific process state, also kept in the database, theactual process state can be determined or approximated. However, theprofile measured during a processing run can fall between two moreprofiles stored in the database. In these cases, interpolation can beused to more accurately determine the conditions (i.e., state) of theprocess. After determining or approximating the process state, themonitor/controller considers the process states corresponding toadjacent values of the parameters in the database. The adjacent processstates are then used to more accurately determine the actual processstate.

[0078] According to one example, if the measured modulation profilecorresponds to a given etching rate in an etching system, and thisetching rate falls directly between the stored modulation profilescorresponding to the two nearest etching rates in the database, aweighted average is taken of the two nearest data points, and anaccurate determination of the actual etching rate can be made. Accordingto another example, if a first stored modulation profile corresponds toan etching process before the completion of the etching, and a secondstored modulation profile corresponds to the same etching process aftercompletion of the etching, then an intermediate modulation profile,between the first and second stored modulation profiles, can correspondto the moment when the etching step is complete or nearly complete. Thisintermediate modulation profile can be calculated from the first andsecond stored modulation profiles, using the interpolation procedure. Bymonitoring the measured modulation profile and determining when itmatches the aforementioned intermediate modulation profile, the momentof completion of the etching step can be accurately determined. Theinterpolation feature provides the advantage that, duringcharacterization of the system, the process conditions tested are notrequired to be extremely close together. Gaps in the data can be “filledin” by either interpolation procedure. This allows the characterizationprocedure to be performed more quickly and allows the system toaccommodate measured profiles which are not identical to storedprofiles.

[0079] In addition to detecting the completion of a processing step, themonitor/controller may be configured so that it can adjust the phase,amplitude, or frequency of the RF power supplied to the respectiveplasma coupling elements. If the system has been characterized wellenough, information can be obtained as to what effect will result fromchanging the characteristics of the power applied to a given plasmacoupling element. If the monitor/controller, by determining themodulation profile during a run, determines that the conditions of theprocess are unsuitable, it is possible to tune the phase, amplitude, orfrequency of the power applied to one or more plasma coupling elementsin order to compensate for this discrepancy. The phase of the RF powercan be adjusted by tuning the variable components in the matchingnetworks. The amplitude and frequency can be tuned by sending a commandto a control circuit in the RF source. By utilizing these techniques,better consistency/repeatability of the process is obtained. Forexample, a system which has processed a number of substrates since thelast cleaning/maintenance operation can be operated to produce the sameresults as a system which has just undergone cleaning/maintenance.

[0080] The advantage of being able to controllably adjust the plasmastate, and therefore the process state, may be more readily appreciatedwith reference to the following examples. According to a first example,a series of test runs has (1) fully characterized an etching process or(2) trained a neural network to control/predict the etching process.During a production run of this process, the monitor/controllerdetermines that, based on measurements of the modulation profile, thecurrent process state does not match the desired process state, and theamount of power received by one of the plasma coupling elements is toolow. As a result, the monitor/controller infers that the etching isproceeding too slowly. The monitor/controller further determines that,based on (1) information in the database or (2) weights in the neuralnetwork, respectively, an increase in the power supplied from one of theRF sources will increase the etching rate. The monitor/controllertherefore increases the amplitude of the power supplied by theappropriate RF source, thereby compensating for the slow etching rate.Alternatively, the monitor/controller may determine that the etchingrate can be increased by tuning the phase of the RF power being receivedby one of the plasma coupling elements. In this case, themonitor/controller tunes the appropriate matching network so as toprovide the necessary phase shift, thereby correcting the problem. Asshould be readily apparent, the technique of monitoring the modulationresponse signals and compensating for any discrepancies provides vastlyimproved control and repeatability of the process and, therefore,improves the consistency of the resulting product.

[0081] A second example relates to an etching process which nominallyuses a gas mixture of, e.g., 30% HCl and 70% Ar. The etching process ofthe second example has been fully characterized by a series of test runsunder a variety of different conditions, including a variety ofdifferent gas mixtures ranging, e.g., from 15% HCl to 50% HCl. During aproduction run of this process, the monitor/controller determines that,based on the measured modulation response signals/modulation profile,the gas mixture of the current process state contains only 20% HCl. As aresult, the monitor/controller infers that the etching rate is too low,and compensates for this by increasing the power supplied from one ofthe RF sources. Alternatively, the flow of HCl gas can be increased.

[0082] The above examples address the effects of insufficient power andincorrect gas mixture. However, the monitor/controller is capable ofcompensating for discrepancies in a variety of different processparameters, such as, but not limited to, gas pressure, systemcleanliness, and RF matching. Although the monitor/controller in theabove examples corrected problems in the process by adjusting the RFpower produced by one of the RF sources, other parameters could also beadjusted including, but not limited to, flow rate of a particular gas inthe mixture (adjusted by sending a signal to a gas flow controller) andgas pressure (adjusted by sending a signal to one or more gas flowcontrollers or by sending a signal to an adjustable valve on an outletport of the chamber), depending upon empirical determinations.

[0083] As should be readily apparent from the foregoing, in accordancewith the present invention, detailed data relating to the plasma stateand system conditions can be obtained. During the performance of aprocess, the data is utilized to monitor the conditions and/or progressof the process, or to detect problems. Precise monitoring of theconditions/progress of the process allows the system to manufacture amore consistent/reliable product. In addition, the early detection ofproblems allows maintenance to be performed promptly to preventwafers/substrate from being processed in an improperly functioningsystem. This also contributes to better quality assurance.

[0084] According to another aspect of the invention, it has beenrecognized that a monitor/controller display can be advantageouslyutilized to provide a human operator with a variety of different data.Examples of data which can be displayed include values or conditions ofmaintenance, of tunable elements in the matching networks, amplitudes orphases of the harmonics or sidebands measured at the respective plasmacoupling elements, relative phases (differences in phases) of two ormore harmonics or sidebands, amplitudes or phases of signals between theharmonics, relative phases of two or more signals between the harmonics,magnitudes or phases of the input impedances of the respective matchingnetworks, light emission at various wavelengths observed coming from theplasma, or graphs of any of these variables as a function of time. Thesegraphs can be displayed in “real-time” (i.e., as time progresses), orthey can be displayed in “event-time”. Event-time is a mode of operationin which a particular event triggers the system to take a sample ofdata. This event may be an arcing incident, the end of a process step,or another user defined event. Other parameters which can be monitoredand displayed, depending on the particular process being observed,include the amount of power demanded by the central process controllerto be sent into the respective plasma coupling elements, the amount ofpower actually measured at the respective plasma coupling elements ortheir respective matching networks, the ratios of various harmonics orof various segments of the broad band frequency spectrum (i.e.,frequency bins), the ratio of the amplitude of a measured harmonic atone node compared to the amplitude of a measured harmonic at anothernode, or broad band signal power in a section of the frequency spectrummeasured at one node compared to signal power in the same section of thefrequency spectrum measured at a different node.

[0085] In a preferred embodiment of the invention, a graph of thespectrum of the signal from a node of the power delivery circuit,including the fundamental, harmonics, and sidebands can be displayed, asillustrated in FIG. 6A. The information can be retrieved at a ratespecified by the user (query mode), at a rate specified by thecontroller (push mode), or using a combination of the two modes.Further, some types of information (e.g., error information) can bespecified as always in push mode so as to bring it to an operator'sattention as soon as possible. In query mode, a self-refreshing WWWbrowser or ActiveX control can be used to periodically collect data in astandard format and display the data. According to another arrangement,illustrated in FIG. 6B, a chart of ratios of the magnitudes of variousharmonics can be displayed in text format. Alternatively, the displaymay combine the views of FIGS. 6A and 6B, or even further views, in asplit screen format (e.g., by using frames in a WWW browser).Furthermore, the views of FIGS. 6A and 6B, or other views, may besequentially alternated in time. It is to be understood that thesedisplay arrangements are examples, and a variety of other displayformats can be utilized.

[0086] The above-described method of displaying data provides theoperator with a clearer understanding of the state of the process, sothat the operator is better able to monitor or control the system anddetect problems before they become damaging, or if damage has alreadyoccurred, its effects can be minimized. As a result, improved productconsistency is obtained, and damage to the system is avoided, therebyreducing maintenance costs.

[0087] As should be readily apparent from the foregoing, the variousaspects and features of the present invention offer several advantagesover those of conventional systems. For example, by providing a detailedand accurate determination of the state/conditions of a process,improved control of the process is achieved. In addition, by thoroughlymonitoring the process, and displaying important data, potentiallydamaging problems can be addressed before the damage occurs or so thatthe damage is minimized. As a result, improved quality control/assuranceand yield, and reduced maintenance costs can be achieved.

[0088] Recently, experimental results taken from a plasma etch chamberhave indicated that harmonic content in electrical signals taken fromplasma coupling elements is a viable diagnostic (or control variable)for impedance matching networks. The investigated plasma etch chamberincludes two independent RF inputs with respective impedance matchingnetworks. The first RF input inductively couples RF energy to a plasmavia a helical coil, and the second RF input provides an RF bias (and DCself-bias) to a substrate via a substrate holding chuck.

[0089] Measurements of the voltage were taken on the primary conductorcarrying RF power from the impedance matching network to the base of thechuck using a Tektronix high voltage probe. The voltage was sampled at200 MHZ for 15 RF periods of a 13.56 MHZ input. The sampling frequencyis sufficient to resolve beyond the fifth harmonic. FIGS. 11A and 11Billustrate a typical Fourier transform (frequency spectrum) of a voltagetime trace in which the fundamental drive frequency, as well as thesecond through fifth harmonics are readily identifiable. In FIGS. 11Athe noise has been removed for clarity. In FIG. 11B, the originalsignal, including noise, is illustrated. Clearly, the harmonic amplitudedecays with increasing harmonic number; however, even the fifth harmonichas a signal-to-noise (S/N) ratio of at least ten. For a given set ofconditions existing within the process chamber, a unique set of harmonicratios can be recorded whereby the harmonic ratios are defined as theharmonic amplitudes at each harmonic frequency normalized by theamplitude of the fundamental (first) drive frequency (i.e., 13.56 MHZ inthe example). The measurement of the ratio of harmonic amplitudes on thechuck was determined to be very repeatable (between conditions, chambermaintenance, etc.) and the error in the measurements was determined tobe less than 5 to 10% for the second harmonic and less than 2.5% for theodd harmonics.

[0090] It has been determined that monitoring the harmonic amplituderatios on the chuck using a high voltage probe can enable the userand/or a feedback controller to tune an impedance matching network forthe RF chuck bias to maximize transmitted power and minimize reflectedpower. FIGS. 12A- 1 3D illustrate harmonic amplitude ratios over athree-dimensional parameter space, wherein the chamber pressure, RFsource power input to the helical coil, and the RF bias power input tothe chuck are varied. A harmonic amplitude ratio E_(n1) has been definedas the ratio of the amplitude of the nth harmonic frequency to theamplitude of the fundamental frequency. For example, FIGS. 12A-12Cillustrate the variation of the ratio E_(2:1) (i.e., for the secondharmonic) as a function of the RF source power at three different RFbias power inputs, i.e., 120 W, 80 W and 40 W, respectively, withchamber pressures ranging from 1 to 20 mTorr. FIG. 12A shows that athigh (120 W) RF bias power, the sensitivity of measurements to thechamber pressure is negligible or within the error limits (in particularfor E_(2:1)). However, as the RF bias power is reduced (as in FIGS. 12Band 12C), a pressure dependence is observable. In particular, a chamberpressure of 20 mTorr causes noticeable change as compared to 10 m Torr.This may be due to greater collisional effects associated with thereduced mean free path at 20 m Torr, which is an order of magnitudegreater than the mean free path at 1 mTorr, and the mean free path'sscale relative to the plasma sheath. In addition, except at low RF biaspower (40 W), there is little dependence of E_(2:1) on the RF biaspower. Therefore, a series of measurements (from prior chambercharacterization) can determine the RF source power input to the helixbased upon E_(2.1).

[0091] FIGS. 13A-13C illustrate measurements for the third harmonic,i.e., E_(3:1). Clearly, the third harmonic is sensitive to the chamberpressure. FIG. 13D illustrates the harmonic amplitude ratio E_(3:1) as afunction of the pressure for a RF source power of 1 kW, and at three RFbias power inputs (40 W, 80 W and 120 W, respectively). Clearly, awell-behaved dependence of E_(3:1) to the pressure an RF bias power isobserved. Therefore, using the information of FIGS. 12A-12C, the RFsource power input from E_(2:1) can be determined, as can the chamberpressure and RF bias power input from FIG. 13D. However, additional datarelationships allow dissociating of the input parameters based upon theharmonic content observed. For example, differences in harmonicamplitude ratios were assessed and determined to perform well inidentifying chamber conditions. In fact, there is nothing limiting thesize of the parameter space, except that the complexity of thecorrelation becomes exceedingly difficult. Specifically, thethree-dimensional space tends to push the bounds to which the data canbe analyzed. At this point, one requires an intelligent control systemcomprising a computer and detection devices that incorporates either apredetermined database of chamber characteristics or a neural network.

[0092] In summary, it has been shown that there exists a directcorrelation between the condition of the plasma and the ratio ofharmonic amplitudes on the substrate holding chuck. Moreover, it hasbeen shown that, for a given system, a subset of harmonic informationcan be used to dissociate between each plasma process input, e.g.,pressure, RF input power to the source and RF input power to the chuck.Hence, the harmonic signature can identify the process inputs and theplasma condition described by these conditions. The subset of harmonicinformation can be composed of any harmonic amplitude ratio, linearcombination of harmonic amplitude ratios, and/or non-linear combinationof harmonic amplitude ratios. More importantly, the harmonic signatureon a plasma coupling element, or combination of elements, can be used tocorrelate with physical parameters that directly affect the process,i.e., ion energy, ion energy distribution, plasma density, chemicalspecies, etc. When referring to a combination of plasma couplingelements, the use of harmonic amplitudes and their ratios to theamplitude of the fundamental frequency is not limited to the chuck butcan be applicable to a variety of electrical plasma coupling elements,e.g., helical coil, bias shield, etc.

[0093] Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

1. A plasma system comprising: a power source; a first plasma couplingelement for providing power from said power source to a plasma; a powervarying controller for modulating at least one of an amplitude, afrequency, and a phase of said power to produce a modulation profile;and a monitoring sensor for receiving said modulation profile of saidfirst plasma coupling element, wherein said modulation profile is causedby said power varying controller.
 2. The system as claimed in claim 1,wherein said monitoring sensor comprises a frequency sensor formeasuring a first detected characteristic of a first component of saidmodulation profile at a first frequency and a second detectedcharacteristic of a second component of said modulation profile at asecond frequency; said system further comprising: a memory for storingstored data, said stored data including a first stored characteristicand a second stored characteristic, wherein said first storedcharacteristic corresponds to said first predetermined frequency andsaid second stored characteristic corresponds to said secondpredetermined frequency; and a central processing unit which compares atleast one of said first detected characteristic and said second detectedcharacteristic to at least one of said first stored characteristic andsaid second stored characteristic, wherein said first detectedcharacteristic, said first stored characteristic, said second detectedcharacteristic and said second stored characteristic are each at leastone of an amplitude and a phase.
 3. The system as claimed in claim 1,further comprising a visual display for displaying at least one of: anamplitude of a component of said modulation profile; a phase of acomponent of said modulation profile; a ratio of (1) a first amplitudeof a first component of said modulation profile and (2) a secondamplitude of said second component of modulation profile; and a relativephase of a first component of said modulation profile with respect to asecond component of said modulation profile, said relative phase being adifference of (1) a phase of said first component and (2) a phase ofsaid second component.
 4. The system as claimed in claim 1, wherein saidmonitoring sensor comprises a frequency sensor for measuring, at adetection time, a first detected characteristic of a first component ofsaid modulation profile at a first predetermined frequency; said systemfurther comprising: a memory for storing stored data, said stored dataincluding first and second stored characteristics corresponding to saidfirst predetermined frequency; and a central processing unit whichcompares said first detected characteristic to said first and secondstored characteristics, wherein all of said first detectedcharacteristic and said first and second stored characteristics are atleast one of an amplitude and a phase, wherein said first and secondstored characteristics corresponds to first and second conditions of aprocess parameter of said plasma process, respectively, and wherein saidprocess parameter is at least one of: progress of the process; iondensity of the plasma; gas mixture of the plasma; gas pressure of theplasma; proper assembly of an electrical component coupled to theplasma; cleanliness of the chamber; thickness of a coating on a surfacewithin the chamber; and quality of matching of a plasma coupling elementto the power source.
 5. The system as claimed in claim 1, wherein saidplasma coupling element comprises at least one of: an electrode; aninductive coil; a bias shield; and an electrostatic chuck.
 6. The systemas claimed in claim 2, wherein said modulation profile includes asideband component caused by said power varying controller, saidsideband component occurring at a frequency corresponding to at leastone of: (a) a sideband frequency of a fundamental frequency of saidpower source; and (b) a sideband frequency of a harmonic frequency ofsaid fundamental frequency.
 7. The system as claimed in claim 3, whereinsaid modulation profile includes a sideband component caused by saidpower varying controller, said sideband component occurring at afrequency corresponding to at least one of: (a) a sideband frequency ofa fundamental frequency of said power source; and (b) a sidebandfrequency of a harmonic frequency of said fundamental frequency.
 8. Thesystem as claimed in claim 4, wherein said modulation profile includes asideband component caused by said power varying controller, saidsideband component occurring at a frequency corresponding to at leastone of: (a) a sideband frequency of a fundamental frequency of saidpower source; and (b) a sideband frequency of a harmonic frequency ofsaid fundamental frequency.
 9. The system as claimed in claim 1, furthercomprising a second plasma coupling element coupled to said plasma. 10.The system as claimed in claim 9, wherein said modulation profileincludes a sideband component caused by said power varying controller,said sideband component occurring at a frequency corresponding to atleast one of: (a) a sideband frequency of a fundamental frequency ofsaid power source; and (b) a sideband frequency of a harmonic frequencyof said fundamental frequency.
 11. A method of controlling a plasmasystem, the method comprising the steps of: providing a power source;providing a plasma coupling element; providing power from said powersource to a plasma; modulating at least one of an amplitude, afrequency, and a phase of said power in order to produce a modulationprofile of said plasma coupling element; and receiving said modulationprofile.
 12. The method as claimed in claim 11, further comprising thesteps of: measuring a first detected characteristic of a first componentof said modulation profile at a first frequency; measuring a seconddetected characteristic of a second component of said modulation profileat a second frequency; storing stored data, said stored data including afirst stored characteristic and a second stored characteristic, whereinsaid first stored characteristic corresponds to said first frequency andsaid second stored characteristic corresponds to said second frequency;and comparing at least one of said first detected characteristic andsaid second detected characteristic to at least one of said first storedcharacteristic and said second stored characteristic, wherein said firstand second detected characteristics and said first and second storedcharacteristics are at least one of an amplitude and a phase.
 13. Themethod as claimed in claim 11, further comprising the steps ofdisplaying at least one of: an amplitude of a component of saidmodulation profile; a phase of a component of said modulation profile; aratio of (1) a first amplitude of a first component of said modulationprofile and (2) a second amplitude of a second component of saidmodulation profile; and a relative phase of a first component of saidmodulation profile with respect to a second component of said modulationprofile, said relative phase being a difference of (1) a phase of saidfirst component and (2) a phase of said second component.
 14. The methodas claimed in claim 11, further comprising the steps of: processing afirst substrate; measuring a first detected characteristic of acomponent of said modulation profile at a frequency corresponding to afirst value of a process parameter, and wherein said process parameteris at least one of: (1) progress of a process; (2) ion density of theplasma; (3) mixture of the plasma; (4) gas pressure of the plasma; (5)proper assembly of an electrical component coupled to the plasma; (6)cleanliness of the chamber; (7) thickness of a coating on a surfacewithin the chamber; and (8) quality of matching of a plasma couplingelement to the power source; storing said first detected characteristic;processing a second substrate; measuring a second detectedcharacteristic of a component of said modulation profile at saidfrequency corresponding to a second value of said process parameter;storing said second detected characteristic; processing a thirdsubstrate; measuring a third detected characteristic of said modulationprofile at said frequency; and comparing said third detectedcharacteristic to said first and second detected characteristics inorder to analyze said modulation profile for said third substrate,wherein said first, second and third detected characteristics are atleast one of an amplitude and a phase.
 15. The method as claimed inclaim 12, wherein said step of varying comprises modulating at least oneof an amplitude, a frequency, and a phase of said power in order toprovide a sideband component of said modulation profile of said plasmacoupling element, wherein said sideband component is at a frequencycorresponding to at least one of: (a) a sideband frequency of afundamental frequency of said power source; and (b) a sideband frequencyof a harmonic frequency of a fundamental frequency of said power source.16. The method as claimed in claim 14, wherein said step of varyingcomprises modulating at least one of an amplitude, a frequency, and aphase of said power in order to provide a sideband component of saidmodulation profile of said plasma coupling element, wherein saidsideband component is at a frequency corresponding to at least one of:(a) a sideband frequency of a fundamental frequency of said powersource; and (b) a sideband frequency of a harmonic frequency of afundamental frequency of said power source.
 17. A plasma systemcomprising: a power source; a first plasma coupling element forproviding power from said power source to a plasma; a power varyingcontroller for modulating at least one of an amplitude, a frequency, anda phase of said power to produce a modulation profile; and a monitoringsensor for receiving the modulation profile, wherein the modulationprofile includes a sideband component caused by the modulation at afrequency corresponding to at least one of: (a) a sideband frequency ofa fundamental frequency of said power source; and (b) a sidebandfrequency of a harmonic frequency of said fundamental frequency.
 18. Ina method of controlling a power source for a plasma coupling element ofa plasma system, the improvement comprising: modulating at least one ofan amplitude, a frequency, and a phase of power delivered by a powersource to a plasma coupling element in order to produce a modulationprofile; receiving said modulation profile; and controlling said powersource based on said modulation profile, wherein said modulation profileincludes a sideband component caused by the modulation, at a frequencycorresponding to at least one of: (a) a sideband frequency of afundamental frequency of said power source; and (b) a sideband frequencyof a harmonic frequency of a fundamental frequency of said power source.